Optical fiber is a very popular medium for large bandwidth applications, and as a result there is a demand for fiber optic cables with greater numbers of optical fibers. In response to demands for increased optical fiber count in fiber optic cables, optical fiber ribbons have been developed. Optical fiber ribbons are planar arrays of optical fibers that are bonded together as a unit. Optical fiber ribbons are advantageous because many ribbons can be stacked on top of each other to form a stack of optical fiber ribbons.
It is conventional for stacks of optical fiber ribbons to be incorporated into two different types of fiber optic cables that are generally referred to as "central-core" and "loose-tube" cables. In the central-core design, a stack of optical fiber ribbons is contained within a central tube that is located at the center of the fiber optic cable. Strength members are positioned between the central tube and an outer plastic jacket of the cable. In contrast, loose-tube fiber optic cables typically include a number of relatively small buffer tubes that are positioned around a central strength member, and each buffer tube encloses a stack of optical fiber ribbons. The buffer tubes are longitudinally stranded around the central strength member, meaning that the buffer tubes are rotated around the central strength member along the length of the fiber optic cable.
It is conventional for the above-referenced tubes to provide at least some protection for the optical fibers therein. It is important for optical fibers to be protected from stain because strain can degrade the performance of the optical fibers. For example, it is conventional for the above-referenced tubes to be round, and for the stacks of optical fiber ribbons to be generally rectangular. Therefore, for each tube and the stack of optical fiber ribbons it contains, there is space defined between the interior surface of the tube and the periphery of the stack. In some applications that space is utilized to allow for relative movement between the stack of optical fiber ribbons and the tube, and that relative movement diminishes the stresses to which the optical fibers are exposed. However, in some applications that space can be characterized as wasted space. In some applications that space is filled with a gel, such as a thixotropic gel, that cushions the stack of optical fiber ribbons to diminish the stresses to which the optical fibers are exposed. However, in some applications those gels are considered a nuisance because they are messy and must be dealt with when entering a fiber optic cable for the purpose or inspection, for forming a splice between optical fibers, or the like. In addition, for a generally rectangular stack of optical fiber ribbons within a round tube, the optical fibers at the corners of the stack will often bear the brunt of any stresses.
Whereas there are several different conventional approaches for protecting stacks of optical fiber ribbons from stress by enclosing the stacks in tubes, further improvements in this area would be beneficial.